The present invention relates to a power transmission belt using ethylene-xc3xa1-olefin elastomer as a constructional member of its belt body. More specifically, the present invention relates to a power transmission belt whose body is formed of a rubber composition of ethylene-xc3xa1-olefin elastomer having an excellent processability (roll processability, tacking ability between rubber sheets, and handling properties of rubber sheets) and that has an excellent running durability.
Examples of industrially used ethylene-xc3xa1-olefin elastomer include ethylene-propylene copolymer (EPM) and ethylene-propylene-diene terpolymer (EPDM). Such polymer has an excellent heat resistance, cold resistance and ozone resistance, is comparatively inexpensive and allows high filler loading. Furthermore, the polymer puts little load on the environment because it is free from halogen elements, and therefore it is used for many applications such as roofing materials, hoses, gaskets, weather strips and the like.
In General, in the applications for roofing materials or the like, the properties of crack resistance (fatigue resistance), abrasion resistance and low heat generation of a vulcanized rubber composition are not important, because it is used in a static situation where there is no repetition strain. Therefore, the rubber composition used for these applications is generally a blended composition of high filler loading to which oil and filler are blended in a large amount. If this kind of rubber composition is used as it is for an application such as a power transmission belt to which dynamic load is applied, the above properties are extremely poor, so that such a belt cannot be practical with respect to its durability. On the other hand, if a rubber composition of low filler loading containing a large amount of a rubber component is applied, the above properties are improved. However, there is the problem that the processability (the roll processability, the tacking ability between rubber sheets and the handling properties of rubber sheets) of the rubber composition in an unvulcanized state is extremely poor. As in the case of a V-ribbed belt, when a high modulus of elasticity in the traverse direction of the belt and a flexibility in the longitudinal direction of the belt are required, the rubber composition constituting the belt body is generally reinforced with short fibers so that the composition has an anisotropy in the elasticity. However, the processability of the rubber composition in which short fibers are mixed is extremely poor.
It is an object of the present invention to provide a power transmission belt whose belt body is formed of a rubber composition of ethylene-xc3xa1-olefin elastomer having an excellent processability and having an excellent running durability.
Moreover, in the present invention, as a raw material rubber of the rubber composition constituting the belt body of the power transmission belt, ethylene-xc3xa1-olefin elastomer containing a predetermined amount of a high molecular weight component and a low molecular weight component, each of which having a predetermined ethylene content, and having a Mooney viscosity of a predetermined value or less is used.
More specifically, the present invention provides a power transmission belt including a belt body composed of a rubber composition containing ethylene-xc3xa1-olefin elastomer as a raw material rubber. The ethylene-xc3xa1-olefin elastomer as the raw material rubber includes 7 to 12 mass % of a high molecular weight component having a molecular weight of 106 or more and an ethylene content of 65 mass % or more, and 26 to 60 mass % of a low molecular weight component having a molecular weight of 105 or less and an ethylene content of 60 mass % or less. The ethylene-xc3xa1-olefin elastomer has a Mooney viscosity of 50 ML1+4 or less (100 C.).
With this embodiment, a constitution distribution of the raw material rubber is appropriate, so that the roll processability, the tacking ability between the rubber sheets and the handling properties of the rubber sheets of the unvulcanized rubber composition before molding the belt are excellent. Furthermore, the running durability of the belt, especially at low temperatures, is more excellent than before.
In other words, if the content of the high molecular weight component having a molecular weight of 106 or more is larger than 12 mass %, the viscosity of the unvulcanized rubber composition before molding into a belt is high and the roll processability and the like are extremely poor. On the other hand, if the content is smaller than 7 mass %, the strength of the unvulcanized rubber composition before molding into a belt is low, so that the rubber is stretched and cut off during molding of a belt. Moreover, the dynamic strength as the vulcanized rubber composition is low after molding of the belt. As a result, the running durability of the belt is extremely poor.
If the content of the low molecular weight component having a molecular weight of 105 or less is larger than 60 mass %, the strength of the unvulcanized rubber composition before molding into a belt is low, so that the rubber is stretched and cut off during molding into a belt. Moreover, the dynamic strength as the vulcanized rubber composition is low after molding of the belt. As a result, the running durability of the belt is extremely poor. On the other hand, if the content is smaller than 26 mass %, the viscosity of the unvulcanized rubber composition before molding into a belt is high, and the roll processability is extremely poor. At the same time, the tacking ability of the unvulcanized rubber composition is low, which makes it difficult to mold into a belt.
If the ethylene content of the high molecular weight component is smaller than 65 mass %, the strength of the unvulcanized rubber composition-before molding into a belt is low and the rubber is stretched and cut off during molding into a belt.
If the ethylene content of the low molecular weight component is larger than 60 mass %, the elastomer increases the crystallinity, the tacking ability of the unvulcanized rubber composition before molding into a belt is low, which makes it difficult to mold into a belt. In addition, the cold resistance of the belt is poor because the belt body is crystallized and becomes rigid at low atmosphere temperatures. In these respects, it is preferable that the ethylene content of the low molecular weight component is 55 mass % or less.
If the Mooney viscosity is higher than 50 ML1+4 (100 C.), the roll processability of the unvulcanized rubber composition before molding into a belt is poor, and the tacking ability is low, so that the molding processability of the belt is poor.
Examples of the ethylene-xc3xa1-olefin elastomer as the raw material rubber include ethylene-propylene copolymer (hereinafter, referred to as xe2x80x9cEPMxe2x80x9d) or ethylene-propylene-diene terpolymer (hereinafter, referred to as xe2x80x9cEPDMxe2x80x9d) or ethylene octene copolymer. Among these, EPDM is preferable.
The rubber composition composed of the ethylene-xc3xa1-olefin elastomer as the raw material rubber may contain short fibers such as nylon fibers, aramid fibers or the like. Since the raw material rubber used in the present invention has a low Mooney viscosity and an excellent rubber flowability, the shear stress applied to the unvulcanized rubber composition during kneading is small and the short fibers are not easily cut off. Therefore, an effect of mixing the short fibers in the rubber composition can be obtained appropriately. For example, if a ribbed rubber layer of the V-ribbed belt is composed thereof, the modulus of elasticity is high in the oriented direction of the short fibers (in the traverse direction of the belt) and the short fibers do not easily fall off while the belt is running. As a result, a loss of the belt caused by abrasion is small, no abrasion due to adhesion occurs and the noise level during running of the belt is low.
Furthermore, examples of power transmission belts of the present invention include V belts, V-ribbed belts, toothed belts and flat belts. In particular, the present invention can be used preferably for V-ribbed belts or toothed belts.
This and other objects and advantages of the present invention will become apparent upon reading and understanding the following detailed description with reference to the accompanying figures.